Cat Spraying - Mount Laurel,NJ

I have a 14 year old male neutered cat. My mother-in-law is terminally ill, and she asked us to take her female 12 year old spayed cat. I begged my husband to say "no". My mother-in-law's cat is so affectionate, and could easily be put up for adoption. My husband ended up bringing his mom's cat to our house to live without even telling me until he showed up with the cat carrier. My cat started spraying all over the place. We took him to the vet, so we know the problem is behavioral and not physical. Since then: I have used every type of cleaning product on the market, as well as natural solutions. I now have three littlerboxes in our very very small house, where it had been hard to find space for just one. I have figured out a way to keep the cats separated. I started using Feliway diffusers and spray. I had decent results with the Feliway - episodes diminished from once or twice a day to once a week. However, we are watching a very tight budget and honestly cannot keep buying the Feliway. One diffuser lasts two weeks and costs quite a bit of money. The vet put my cat on medication, which is also helping. We have hardwood floors, and he is not allowed in rooms with carpeting, so at least we don't have to worry about carpet. His main spots now are doormats and bathroom contour rugs in front of the toilet. I have gotten rid of those. I like the way they look and feel, but I'd rather have my cat than the rugs. I put mats outside the door to wipe our feet, but there is one entrance in a high traffic area where we really could use a mat inside the door as well, to protect our floors. I suggested just taking our shoes off when we come in, but my husband has a lot of foot problems, and refuses to take his shoes off in the house. We just bought new curtains for our sliding glass door. They touch the floor a little bit, and the cat sprayed on those. The worst part is that my husband will not helpwith the cleaning or problem solving. I think that every time I mention the problem, it reminds him of the situation with his mom, and he just shuts down or gets mad at me. He wants me to put my cat to sleep. Our 9 year old son doesn't seem to care, because the cat peed on some of his toys before I started using Feliway. Basically, I am this cat's only friend right now. I can't bear the thought of putting this cat down, but I am tired of cleaning, spending extra money we don't have, and smelling cat pee when I walk in the house. Last night he peed in front of the toilet where the rug used to be. My friend, who is a vet, said not to let the situation come between me and my husband, and that if I put him down I shouldn't feel bad because I have tried everything. Is it time to say good-bye to my 14 year old feline? I am worried that when we go away for a weekend he will pee and it won't get cleaned up right away. Thanks!